Temporary implantable medical electrical leads are often employed to evaluate the efficacy of electrical stimulation prior to implanting a chronically implantable stimulation system within a patient. For example, the efficacy of sacral nerve stimulation in patients, for the treatment of urinary incontinence, is evaluated with what is known as trialing or a percutaneous nerve evaluation (PNE) lead, which is temporarily implanted, via a minimally invasive procedure, for an evaluation period, for example, of up to approximately 7 days, depending upon the particular patient. Implant access to the sacral nerves is typically gained via fluoroscopic and/or ultrasound guidance of a spinal needle that is percutaneously inserted, from a posterior side of the sacrum, through a foramen thereof and into the region of the sacral nerves; the PNE lead is then inserted through a lumen of the needle such that a stimulating electrode of the lead contacts a sacral nerve.
An example of a PNE lead, which is known in the art, is shown in the section view of FIG. 1. FIG. 1 illustrates a unipolar PNE lead 700 that includes a conductor coil 75 formed from a single wire filar would around a lumen of lead 700. The wire filar is preferably formed as a cable, by a plurality of wire strands, for example, seven wire strands, that are braided together; and the wire filar has an insulative coating, for example, formed from a fluoropolymer material, that provides electrical isolation along a majority of the length of conductor 75. The insulative coating is removed from the wire filar along a distal length of conductor 75 to form a stimulating electrode 750 of lead 700. The insulative coating is also removed from the wire filar at a proximal end of coil 75, where a junction/coupling is formed with a connector 73 of lead 700. According to FIG. 1, the coupling is enclosed within a tubular member 78, which may be formed from a heat shrinkable polymer material, such as polyester.
When lead 700 is temporarily implanted in a patient, for example, such that electrode 750 contacts a sacral nerve, and when a ground pad is coupled to the patient's epidermis, connector 73, which remains extracorporeal (outside the patient's body), may be coupled to a stimulation source in order to deliver unipolar stimulation to the nerve via electrode 750. If stimulation from lead 700 is found effective for a particular placement of electrode 750 in the patient, lead 700 is replaced with a chronically implantable lead that is part of a chronically implantable system. Examples of such a chronically implantable lead include the Model 3093 and the Model 3889, both of which are quadripolar leads available from Medtronic, Inc.
Although the prior art lead 700 has been found useful, there remains a need for new and improved designs of temporary implantable medical electrical leads.